A double-blind, controlled clinical trial in 1,955 evaluable women compared the efficacy and safety of levonorgestrel tablets, (one 0.75 mg tablet of levonorgestrel taken within 72 hours of intercourse, and one tablet taken 12 hours later) to the Yuzpe regimen (two tablets of 0.25 mg levonorgestrel and 0.05 mg ethinyl estradiol, taken within 72 hours of intercourse, and two tablets taken 12 hours later). Levonorgestrel tablets, were at least as effective as the Yuzpe regimen in preventing pregnancy. After a single act of intercourse, the expected pregnancy rate of 8% (with no contraception) was reduced to approximately 1% with levonorgestrel tablets.

Emergency contraceptives are not as effective as routine contraception since their failure rate, while low based on a single use, would accumulate over time with repeated use (see WARNINGS). See Table 2 below.

Table 2 Percentage of women experiencing an unintended pregnancy during the first year of typical use and the first year of perfect use of contraception, and the percentage continuing use at the end of the first year, United States.

% of Women Experiencing an Unintended Pregnancy within the First Year of Use

1 Among typical couples who initiate use of a method (not necessarily for the first time), the percentage who experience an unintended pregnancy during the first year if they do not stop use for any other reason.

2 Among couples who initiate use of a method (not necessarily for the first time) and who use it perfectly (both consistently and correctly), the percentage who experience an unintended pregnancy during the first year if they do not stop use for any other reason.

3 Among couples attempting to avoid pregnancy, the percentage who continue to use a method for one year.

4 The percentages of women becoming pregnant in columns (2) and (3) are based on data from populations where contraception is not used and from women who cease using contraception in order to become pregnant. Among such populations, about 89% become pregnant within one year. This estimate was lowered slightly (to 85%) to represent the percentage who would become pregnant within one year among women now relying on reversible methods of contraception if they abandoned contraception altogether.

5 Foams, creams, gels, vaginal suppositories and vaginal film.

6 Cervical mucus (ovulation) method supplemented by calendar in the preovulatory and basal body temperature in the post-ovulatory phases.

7 With spermicidal cream or jelly.

8 Without spermicides.

9 The treatment schedule is one dose within 72 hours after unprotected intercourse and a second dose 12 hours after the first dose. The Food and Drug Administration has declared the following brands of oral contraceptives to be safe and effective for emergency contraception: Ovral®* (1 dose is 2 white pills), Alesse®* (1 dose is 5 pink pills), Nordette®* or Levlen®* (1 dose is 2 light-orange pills), Lo/Ovral®* (1 dose is 4 white pills), Triphasil®* or Tri-Levlen®* (1 dose is 4 yellow pills).

10 However, to maintain effective protection against pregnancy, another method of contraception must be used as soon as menstruation resumes, the frequency or duration of breastfeeds is reduced, bottle feeds are introduced or the baby reaches six months of age.

Chance4

85

85

Spermicide5

26

6

40

Periodic Abstinence

25

63

Calendar

9

Ovulation Method

3

Sympto-thermal6

2

Post-ovulation

1

Withdrawal

19

4

Cap7

Parous Women

40

26

42

Nulliparous Women

20

9

56

Sponge

Parous Women

40

20

42

Nulliparous Women

20

9

56

Diaphragm7

20

6

56

Condom8

Female (Reality®*)

21

5

56

Male

14

3

61

Pill

5

71

Progestin Only

0.5

Combined 0.1

0.1

IUD

Progesterone T

2.0

1.5

81

Copper T 380A

0.8

0.6

78

LNg 20

0.1

0.1

81

Depo-Provera®*

0.3

0.3

70

Norplant®* andNorplant-2®*

0.05

0.05

88

Female Sterilization

0.5

0.5

100

Male Sterilization

0.15

0.10

100

Emergency Contraceptive Pills: Treatment initiated within 72 hours after unprotected intercourse reduces the risk of pregnancy by at least 75%.9